1. Field of the Invention
The present invention is directed to a computed tomography apparatus and to a method for operating a computed tomography apparatus, and in particular to an apparatus and operating method for a computed tomography apparatus of the type having a rotating anode x-ray tube.
2. Description of the Prior Art
Computed tomography systems are known which employ a rotating anode x-ray tube as the x-ray source. The rotating anode x-ray tube and a radiation detector are disposed opposite each other on a gantry, which is tiltable perperticular system axis, which is parallel to a support on which an examination subject is disposed. The gantry forms a frame on which the x-ray tube and the radiation detector are mounted, and is also rotatable around the system axis for conducting a scan of the examination subject. The gantry is nominally disposed in a plane perpendicular to the system axis, and is tilted out of this plane so that the plane of the scanned slice can be varied (selected).
Because of the rapid rotation of the anode within the x-ray tube, the rotating anode behaves as a gyroscope. When tilting the rotating gantry, gyroscopic moments (force vectors) act on the anode bearing due to the rotation of the anode around its symmetry axis, as well as due to the rotation of the gantry around the system axis. These gyroscopic moments reside perpendicular to a plane defined by the respective rotational axis and the outer tilting moment.
In known computed tomography systems of this type, the rotational direction of the anode and the rotational direction of the gantry are in the same direction. As a result, the gyroscopic forces are cumulative (add together), resulting in a high mechanical stressing of the anode bearing.